ajv@6.4.0 doesn't support Node v4

[teppeis]

In Node.js v4, yarn cannot install ajv:

$ yarn add ajv
yarn add v1.5.1
[1/5] 🔍  Validating package.json...
[2/5] 🔍  Resolving packages...
[3/5] 🚚  Fetching packages...
error punycode@2.1.0: The engine "node" is incompatible with this module. Expected version ">=6".                                               
error An unexpected error occurred: "Found incompatible module".
info If you think this is a bug, please open a bug report with the information provided in "/Users/teppeis/src/github.com/teppeis/kintone-plugin-manifest-validator/yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.

also npm warns:

$ npm install ajv
npm WARN engine punycode@2.1.0: wanted: {"node":">=6"} (current: {"node":"4.8.7","npm":"2.15.11"})
ajv@6.4.0 node_modules/ajv
+-- json-schema-traverse@0.3.1
+-- fast-deep-equal@1.1.0
+-- fast-json-stable-stringify@2.0.0
`-- uri-js@3.0.2 (punycode@2.1.0)

544 introduces uri-js and it requires punycode that doesn't support Node v4.

IMO ajv can drop support Node v4 (the EOL is next month, April 2018). It would be better to add engines field to package.json of ajv.

[epoberezkin]

It looks like yarn problem, npm installs it ok: https://travis-ci.org/epoberezkin/ajv/jobs/358014029

[teppeis]

@epoberezkin yes, exit with an error is yarn's expected behavior (and it has --ignore-engines option for the workaround). But also npm shows warning. https://travis-ci.org/epoberezkin/ajv/jobs/358014029#L462

Anyway, punycode (and uri-js) dropped support for Node v4. https://github.com/bestiejs/punycode.js/pull/48

But according to README, ajv supports Node.js 0.10+.

supports browsers and Node.js 0.10-8.x

[epoberezkin]

README indeed need updating